Apparatus for printing on curved surfaces

ABSTRACT

A printer for cups or similar articles, or articles with a surface of revolution having a straight line generatrix, has a helical printing plate. The articles are advanced along a line parallel to the axis of the plate and the sidewall is imprinted while it follows a substantially helical path. Cups or containers are fed through in partially nested condition.

O Unlted States Patent [151 3,66 1,075 Amberg 1 May 9, 1972 541 APPARATUS FOR PRINTING 0N 2,104,044 1/1938 King ..101/36 x CURVED SURFACES 1,781,793 11/1930 Spencer ..101/375 ux 707,540 8/1902 Baruch [721 Amberg James 2,047,718 7/1936 Von Webern. ..101 [36 x [73] Assignee: Owens-Illinois, Inc. 2,890,787 6/1959 Carter.... ..l98/34 A 2,433,736 12/1947 Carew ..22l/222 [22] F1led: Dec. 5, 1969 [21 1 Appl' 882539 Primary Examiner-Robert E. Pulfrey Asxistam Examiner-Clifiord D. Crowder [52] US. Cl ..101/40, 101/376, 101/426, Attorney-Brooks. Haidt & Haffner 198/34, 214/8.5 H, 221/222 [51] Int. Cl. ..B4lf 17/28, B41f 17/20 [58] Field of Search ..1o1/35 40, 375-377, [57] ABSTRACT l 8, 219; 82/531, 46, 59 70, 101, 102; A printer for cups or s1m1lar artlcles, or artlcles with a surface 221/221 223, 198/34 214/85 R of revolution having a straight line generatrix, has a helical 1 18/DIG 2O, DIG. DIG 22 14, DIG printing plate. The articles are advanced along a line parallel to the axis of the plate and the sidewall is imprinted while it follows a substantially helical path. Cups or containers are fed 5 References Cited through in partially nested condition.

UNITED STATES PATENTS 17 Claims, 4 Drawing Figures 3,442,364 5/1969 Ragen ..l97/49 2,592,667 4/1952 Donnan ..1 18/234 X a v Q PATENTEDHAY 9 1922 SHEET 1 OF 2 1 N VEN T OR. STEP/l6 4/ 4,

PO PO PATENTEDMAY 9 m2 SHEET 2 []F 2 I N VEN TOR. 576996 4 Avaam APPARATUS FOR PRINTING ON CURVED SURFACES The present invention relates to printing and, more particularly, to printing on a surface of revolution.

The invention has been applied satisfactorily to the printing of the sidewall of cup-shaped articles, namely, plastic cups. While the invention is not limited thereto, as will appear from the ensuing description, it will be described basically in terms of the printing of such cups although it is believed that it will be readily appreciated that the invention can be applied to the printing of any print receiving surface represented by a surface of revolution with a straight line generatrix.

Heretofore, a typical arrangement for printing the sidewall of an already formed cup made use of a turret array of mandrels, each for supporting the interior of an individual cup while the sidewall was brought into contact with a printing element which was in the form of either a cylindrical, a frustoconical, or a circular printing plate. The maximum speed of operation of such known cup printing equipment was necessarily limited. Hence, it was not suited to use directly in line with the cup forming equipment.

It is, therefore, an object of the present invention to provide an efficient arrangement for post printing plastic or paper cups or containers at a production rate in excess of 750 per minute with at least a single color flexographic imprint.

It is a further object ofthe invention to provide a method of decorating the sidewalls of cups or containers which is more economical than methods known heretofore.

A still further object of the invention is to provide a cup printing machine which can be employed efficiently in line with known cup forming equipment.

The present invention is based upon the discovery of a method of printing the sidewalls of cups or containers while they remain in partially nested condition. The method requires no back-up roll or platen nor does it require the individual mounting of the cup or container on a mandrel or arbor. Instead, in accordance with one aspect of the invention, there is provided apparatus for printing which comprises means for supporting a helical printing plate, and means for feeding the medium to be printed past the plate supporting means with its print receiving surface following a path which is at least approximately helical.

In accordance with a further aspect of the invention, there is provided apparatus for conveying a cup-shaped article having a radially extending rim comprising three cylindrical members mounted for synchronized rotation about individual parallel axes all spaced equidistant from a central axis defining a chute-like path therebetween for receiving and confining the article therealong, each cylindrical member being provided with helical means for engaging the rim of the article, the feed rates of all of the helical means at any given point along the chute-like path being identical at such point with the exception of a section of the helical means of one cylindrical member, said section having a different feed rate from the corresponding feed rate at the same point along the chute-like path of the other helical means for canting the article as it passes said section.

The invention will be better understood after reading the following detailed description of the presently preferred embodiments thereof with reference to the appended drawings wherein:

FIG. 1 is a simplified elevational view, somewhat diagrammatic, showing the basic components for feeding the cups or containers and for printing the sidewalls thereof;

FIG. 2 is a plan view, also diagrammatic, of the structure of FIG. 1 with the upper feed cylindrical member removed for clarity;

FIG. 3 is a fragmentary sectional view taken along the line 3-3 in FIG. 2 and showing a detail thereof; and

FIG. 4 is a diagrammatic view showing a modification of the equipment for two-color printing.

Throughout the figures of the drawings, the same reference numerals are used to designate the same or similar parts.

Referring specifically to FIG. 1, the structure may be divided into two basic units, the printing section shown generally to the left, and the cup feeding section shown generally to the right. The printing section is made up of an inkwell 10, a fountain roll 11, an ink transfer roll 12, a print cylinder 13, and a helical printing plate 14. It is believed that the elements 10, 11, 12 and 13 are conventional. They are arranged on individual shafts for rotation in rolling contact as seen in the drawings. The elements 10 through 13 may be mounted on a common carriage (not shown) for adjustable movement toward or away from the nested stack of cups to be printed which are designated by the reference numeral 15. For further flexibility and control in known manner, the elements 10, 11 and 12 may be mounted on a sub-carriage for movement into and out of engagement with the printing plate 14 which is mounted on the print cylinder 13, the latter being mounted on the main carriage.

While it may be considered as forming a part of the cup feeding section, a pair of guide roads or rollers 16 and 17 is mounted on the main carriage for movement toward and away from the cup printing zone with the print cylinder 13.

The cup feeding section comprises additionally three cylindrical members 18, 19 and 20 mounted for synchronized rotation about individual parallel axes all spaced equi-distant from a central axis defining a chute-like path therebetween for receiving and confining the cups 15 therealong. The cylindrical member 18 has its shaft 21 mounted for rotation in fixed position on a frame 22. The member 19 has its shaft 23 mounted for rotation in the end of adjustable arms, one of which is shown at 24, the other end of the arms being pivotally mounted on the frame 22. This permits the position of the cylindrical member 19 to be adjusted toward or away from the chute-like axis for accommodating cups of different diameter. In similar manner, the cylindrical member 20 has its shaft 25 mounted at the end of arms, one of which is shown at 26, which have their other ends pivotally mounted on frame 22.

The cylindrical members 19 and 20 are identical in construction. Hence, only the member 20 is shown in FIG, 2, to which attention is now directed. It will be seen from FIG. 2 that each cylindrical member is provided with helical means in the form of grooves 27 or 28 for engaging the rims 29 of the individual cups. The cups enter the chute-like path in fully nested condition at 30 and leave the path at 31 in the manner shown, For a short distance through a zone 32, the three cylindrical members 18, 19 and 20 are of identical construction with helical grooves having a lead related to the configuration of the cups to just slightly denest the stack. It will be understood that the helical grooves on each of the cylindrical members are appropriately phased relative to one another and are rotating in synchronism to feed the stack uniformly along the axis of the chute-like path.

Throughout a zone 33 the helical lead on all three cylindrical members abruptly increases in identical fashion to partially separate successive cups as they pass through this zone. This serves to expose a print receiving surface on the sidewalls of the cups.

For the sake of discussion, it may be assumed that the helical grooves in the zone 32 on the three cylindrical members 18, 19 and 20 each have a lead equal to a It may also be assumed that the lead of the helical groove on the member 18 in the zone 33 has a lead equal to 1;. Assume also that the helical grooves on the cylindrical members 19 and 20 from the zone 32 to the opposite end of the members have a constant lead also equal to b.

As an important aspect of the present invention, the cylindrical member 18 differs from the members 19 and 20 in a zone 34 wherein the lead of the groove 27 is increased slightly to equal b+c. Thus, as clearly shown in FIG. 2, the cups are gradually canted or tipped as they move from the right to the left as viewed in the drawing until the longitudinal element 35 of the sidewall of the tapered sidewall cup, which element 35 is nearest the print cylinder 13 at any moment, is parallel to the axis of the print cylinder 13. Finally, the helical groove 27 on the cylindrical member 18 returns to the lead b in the zone 36. Thus, throughout the zone 36 the cups are fed without further canting.

All of the members engaging the cups are rotating in the same direction. Hence, due to friction, rotation is imparted to the cups in the opposite direction. It will, therefore, be appreciated that the print receiving surface of the cup sidewall follows a path which is approximately helical. It is only approximately helical because of the canted position of the cup.

To provide more positive feed of the cups, the cylindrical member 18 is provided with a rib 37, best seen in FIG. 3, backing up the helical groove 27 throughout a major portion of the member 18. The rib commences at the interface between the regions 32 and 33. It starts with zero height and gradually increases in height throughout the region 33 reaching its maximum height at the interface between regions 33 and 34. This taper is designed to afford clearance relative to the sidewalls of the cups until they are fully expanded into their partially separated condition.

As seen in FIG. 2, the cylindrical member 18 is preferably formed from four separate cylindrical members 38, 39, 40 and 41 mounted in endto-end relationship on the shaft 21.

it is important that all of the members making contact with the cups do so in a rolling manner without slippage. Hence, the diameters and speeds of rotation of the individual members contacting the cup must be properly related thereto such that the linear speed of each such member at the point of contact with the cup is the same. While not limited thereto, it is convenient to make the cylindrical members l8, l9 and all of the same diameter. Therefore, these members are arranged to rotate at the same angular speed. It is also convenient to drive the print cylinder 13 at the same angular speed as the members 18, 19 and 20. Therefore, the diameter of the helical printing plate 14 must be slightly less than the diameters of the members 18, 19 and 20 because it engages a portion of the cup which is of smaller diameter than the diameter of the rim 29.

Since the printing plate 14 is in the form of a cylindrical helix, while the cup sidewall is frusto-conical, the relationship between printing plate and cup sidewall can only be approximated. Satisfactory results will be obtained by designing the printing plate for proper relationship with the mean circumference 42 between the maximum and minimum circumferences 43 and 44, respectively, defining the limits of the printing zone.

In actual tests, it has been found possible to print satisfactorily without observable smudging a 9% inch wide zone on a plastic cup having a sidewall taper of approximately 7.

Having assumed that the rotating members l3, 18, 19 and 20 all turn at the same angular speed, and that the members 18, 19 and 20 are of larger diameter than the cup rim, the geometry dictates that the helical printing plate 14 occupy less than the total circumference of the print cylinder 13. Obviously, the length of the helical printing plate 14 should be equal to the circumference of the surface to be printed on the cup, assuming that the complete circumference is to be printed without overlap. Since the print cylinder 13 is rotating atthe same angular speed as the cylindrical members l8, l9 and 20, the printing plate 14 should have a lead equal to the lead of the helical groove 28, i.e., the lead b.

In describing the subject apparatus it is convenient to use the term feed rate." This is defined as the product of the lead of the particular helical element and the angular velocity thereof, The feed rates of the members 18, 19 and 20 and of the printing plate 14 must all be identical at any given point along the feed path. The only exception is in the region 34 where the feed rate of the member 18 is increased in order to cant the cups. Of course, if the cups were being fed in reverse direction, that is, with the lips foremost rather than last, the feed rate of the member 18 in the region 34 would be decreased rather than increased.

From FIG. 1 it will be observed that the members 19 and 20 engage the cups at points displaced from the point of contact with member 18 by more than 90 but less than l. This relationship, in combination with the rollers 16 and 17, provides for complete confinement of the cups within the chutelike path. The rollers 16 and 17 only lightly contact the rims of the cups to ensure that they remain within the chute-like path in the region in advance of the printing plate. They also serve the same function after the cups pass beyond the printing plate.

It should be appreciated from the foregoing that the feeding means represented by the members 18, 19 and 20 rotate the cups about their own axes while simultaneously advancing the cups into printing position and through a printing zone along a path parallel to the axis of the print cylinder 13, with each cup oriented as it passes through the printing zone with its own axis in a common plane with the axis of the print cylinder 13 and with the longitudinal element 35 of its sidewall in contact with the printing plate 14. The cylindrical member 18, being mounted on the opposite side of the feed path from the print cylinder 13, maintains the articles or cups as they pass the print cylinder in print receiving contact with the printing plate.

The arrangement shown in FIGS. 1, 2 and 3 provides for one color printing. By using offset techniques it is possible to print in more than one color. Alternatively, use may be made of an arrangement as represented in FIG. 4 to which attention is now directed. As seen therein, the object to be printed is represented by a cylindrical rod or body 45. It is assumed that the body 45 is being rotated and translated in the direction of the respective arrows 46 and 47. A plurality of helical printing plates, here illustrated as the two plates 48 and 49, are mounted in side-by-side co-axial relationship on a printing cylinder 50 which, in turn, is mounted for rotation in the direction of the arrow 51. Each printing plate 48 and 49 is inked by a separate ink transfer roll 52 and 53, respectively. While not shown, it will be appreciated that the transfer rolls 52 and 53 are fed from separate ink supplies.

For the purpose of illustration, it has been assumed in FIG. 4 that the diameter of the printing plates is twice the diameter of the object 45 which is being printed. Hence, the printing plates 48 and 49 each make one-half turn around the circumference of the print cylinder 50. The two plates 48 and 49 are so located that the plate 48 imprints the object 45 as the latter makes one full revolution and advances through the zone 54. As the object advances through the next zone 55, it makes one more complete revolution. Finally, it is imprinted by the plate 49 as it passes the zone 56, again making one complete revolution. It is assumed that the ink applied in the region 54 by the first plate 48 will have had an opportunity to dry as it passes through the region 55 in order to avoid smearing or offsetting. If desired, suitable auxiliary drying means may be employed. Such auxiliary means may also be used with the embodiment described with reference to FIGS. 1,2 and 3.

The arrangement shown with reference to H6. 4 is intended merely by way of example to illustrate the versatility of the subject concept. It is to be understood that while the object 45 is shown as a rod in FIG. 4 it could be a stack of cups as shown in FIG. 1.

Having described the invention with reference to the presently preferred embodiments thereof, it will be appreciated that various changes in construction may be made without departing from the true spirit of the invention.

What is claimed is:

1. Printing apparatus comprising a rotatable print cylinder, a printing plate on said cylinder having a pattern printing surface extending helically around the axis of rotation of said cylinder and facing radially outwardly therefrom, and feeding means for feeding cup-shaped articles past said printing surface and in contact therewith comprising means for rotating said cup-shaped articles about their own axes while simultaneously advancing said articles into printing position and through a printing zone along a path parallel to the axis of the print cylinder with each said article oriented as it passes through the printing zone with its own axis in a common plane with the axis of the print cylinder and with the longitudinal element of its sidewall nearest the print cylinder at any moment being parallel to the axis of the print cylinder and in contact with said printing surface.

2. Apparatus according to claim 1, for imprinting cupshaped articles having tapered sidewalls, wherein said feeding means comprises means for canting each article as it approaches the printing zone to bring said longitudinal element parallel to the axis of said print cylinder,

3. Apparatus according to claim 1, wherein said feeding means comprises means for receiving a nested stack of said articles, and means for partially separating successive articles as they approach the printing zone to expose a print receiving surface on their sidewalls.

4. Apparatus according to claim 3, for imprinting cupshaped articles having tapered sidewalls, wherein said feeding means comprises means for canting each article as it approaches the printing zone to bring said longitudinal element parallel to the axis of said print cylinder.

5. Printing apparatus comprising a rotatable print cylinder, a printing plate on said cylinder having a pattern printing surface extending helically around the axis of rotation of said cylinder and facing radially outwardly therefrom, and feeding means for feeding cup-shaped articles past said printing surface and in contact therewith comprising a plurality of cylindrical members mounted for synchronized rotation about individual axes all parallel to the axis of said print cylinder and defining with said print cylinder a feed path between them for receiving a nested stack of cup-shaped articles, each cylindrical member being provided with helical means for engaging a radially extending lip on said article, the respective helical means being related for rotating the articles of said stack while advancing the stack past said printing surface.

6. Apparatus according to claim 5, wherein said cylindrical members are longer than said print cylinder extending in advance of the latter, and one of said cylindrical members is mounted on the opposite side of said feed path from said print cylinder for maintaining the articles as they pass the print cylinder in print receiving contact with said printing surface, the feed rates of all of said helical means at any given point along the feed path being identical with the exception of a section of the helical means ofsaid one cylindrical member which is in advance of the print cylinder, said section having a different feed rate from the corresponding feed rate at the same point along the feed path of the other helical means for canting each article as it approaches the print cylinder to bring the longitudinal element of the sidewall of a tapered sidewall article, which element is nearest the print cylinder at any moment, into a position parallel to the axis of the print cylinder.

7, Apparatus according to claim 6, wherein all of said cylindrical members have helical means with the same diameters and are coupled for rotation at the same speed, the leads of all of said helical means at any given point along the feed path being identical with the exception ofsaid section of the helical means of said one cylindrical member.

8. Apparatus according to claim 6, wherein said plurality of cylindrical members comprise two members in addition to said one cylindrical member, said two members being arranged to engage said articles at points spaced more than 90 but less than 180 on opposite sides of the point at which said articles are engaged by said one cylindrical member.

9. Apparatus according to claim 5, including a helical printing plate having a feed rate which is identical at any point in the direction of the feed path with the feed rates of all of said helical means corresponding to the same point.

10. Apparatus for conveying a cup-shaped article having a radially extending rim comprising three cylindrical members mounted for synchronized rotation about individual parallel axes all spaced equi-distant from a central axis defining a chute-like path therebetween for receiving and confining said article therealong each cylindrical member being provided with helical means for engaging said rim of said article, the feed rates of all of said helical means at any given point along the chute-like path being identical at such point with the exception of a section of the helical means of one cylindrical member, said section having a different feed rate from the corresponding feed rate at the same point along the chute-like path of the other helical means for canting the article as it passes said section.

11. Apparatus according to claim 10, wherein said three cylindrical members have helical means with the same diameters and are coupled for rotation at the same speed, the leads of all of said helical means at any given point along the chutelike path being identical with the exception of said section of the helical means of said one cylindrical member.

12. The method of imprinting the sidewall of a cuplike article which comprises the steps of feeding said articles in a nested stack toward a printing zone, partially separating said articles as they approach the printing zone to expose a region of the sidewall for printing, and imprinting said region of each article as it passes the printing zone while the articles are in partially nested condition.

13. The method of claim 12, further comprising the step of canting each article after said partial separation to bring an element of a tapered sidewall in parallel with the direction of travel past the printing zone.

14. Printing apparatus comprising a printing plate mounted for rotation about a predetermined axis, said plate having a pattern printing surface extending helically around said axis and facing radially outwardly therefrom, drive means for rotating said plate around said axis and thereby moving each portion of said printing surface in a circumferential direction around said axis and feeding means for engaging the surface of a medium to be printed on with said printing surface and for simultaneously moving the portion of said surface of said medium which engages said printing surface both in the same direction and at the same rate as the portion of said printing surface which it engages is moved, thereby to cause them to move without slippage therebetween, and in a direction parallel to the direction of said axis.

15. Apparatus according to claim 14 further comprising a second printing plate having a second pattern printing surface mounted for rotation co-axially with said first-mentioned printing plate but spaced axially therefrom, said second printing surface extending helically around said axis and facing radially outwardly therefrom, drive means for rotating said second plate around said axis and thereby moving each portion of said printing surface in a circumferential direction around said axis and feeding means for engaging the surface of a medium to be printed with said printing surfaces and for simultaneously moving the portion of said surface of said medium which engages said printing surfaces both in the same direction and at the same rate as the portions of said printing surfaces which it engages are moved, thereby to cause them to move without slippage therebetween, and in a direction parallel to the direction of said axis.

16. Apparatus according to claim 15 further comprising first means for inking one of said printing surfaces, and second means for inking the other of said printing surfaces.

17. Apparatus according to claim 14, wherein the medium to be printed has a print receiving surface represented by a surface of revolution with a straight line generatrix, and said feeding means comprises means for orienting said medium such that its print receiving surface makes rolling line contact with said printing surface. 

1. Printing apparatus comprising a rotatable print cylinder, a printing plate on said cylinder having a pattern printing surface extending helically around the axis of rotation of said cylinder and facing radially outwardly therefrom, and feeding means for feeding cup-shaped articles past said printing surface and in contact therewith comprising means for rotating said cup-shaped articles about their own axes while simultaneously advancing said articles into printing position and through a printing zone along a path parallel to the axis of the print cylinder with each said article oriented as it passes through the printing zone with its own axis in a common plane with the axis of the print cylinder and with the longitudinal element of its sidewall nearest the print cylinder at any moment being parallel to the axis of the print cylinder and in contact with said printing surface.
 2. Apparatus according to claim 1, for imprinting cup-shaped articles having tapered sidewalls, wherein said feeding means comprises means for canting each article as it approaches the printing zone to bring said longitudinal element parallel to the axis of said print cylinder.
 3. Apparatus according to claim 1, wherein said feeding means comprises means for receiving a nested stack of said articles, and means for partially separating successive articles as they approach the printing zone to expose a print receiving surface on their sidewalls.
 4. Apparatus according to claim 3, for imprinting cup-shaped articles having tapered sidewalls, wherein said feeding means comprises means for canting each article as it approaches the printing zone to bring said longitudinal element parallel to the axis of said print cylinder.
 5. Printing apparatus comprising a rotatable print cylinder, a printing plate on said cylinder having a pattern printing surface extending helically around the axis of rotation of said cylinder and facing radially outwardly therefrom, and feeding means for feeding cup-shaped articles past said printing surface and in contact therewith comprising a plurality of cylindrical members mounted for synchronized rotation about individual axes all parallel to the axis of said print cylinder and defining with said print cylinder a feed path between them for receiving a nested stack of cup-shaped articles, each cylindrical member being provided with helical means for engaging a radially extending lip on said article, the respective helical means being relatEd for rotating the articles of said stack while advancing the stack past said printing surface.
 6. Apparatus according to claim 5, wherein said cylindrical members are longer than said print cylinder extending in advance of the latter, and one of said cylindrical members is mounted on the opposite side of said feed path from said print cylinder for maintaining the articles as they pass the print cylinder in print receiving contact with said printing surface, the feed rates of all of said helical means at any given point along the feed path being identical with the exception of a section of the helical means of said one cylindrical member which is in advance of the print cylinder, said section having a different feed rate from the corresponding feed rate at the same point along the feed path of the other helical means for canting each article as it approaches the print cylinder to bring the longitudinal element of the sidewall of a tapered sidewall article, which element is nearest the print cylinder at any moment, into a position parallel to the axis of the print cylinder.
 7. Apparatus according to claim 6, wherein all of said cylindrical members have helical means with the same diameters and are coupled for rotation at the same speed, the leads of all of said helical means at any given point along the feed path being identical with the exception of said section of the helical means of said one cylindrical member.
 8. Apparatus according to claim 6, wherein said plurality of cylindrical members comprise two members in addition to said one cylindrical member, said two members being arranged to engage said articles at points spaced more than 90* but less than 180* on opposite sides of the point at which said articles are engaged by said one cylindrical member. Apparatus according to claim 5, including a helical printing plate having a feed rate which is identical at any point in the direction of the feed path with the feed rates of all of said helical means corresponding to the same point.
 10. Apparatus for conveying a cup-shaped article having a radially extending rim comprising three cylindrical members mounted for synchronized rotation about individual parallel axes all spaced equi-distant from a central axis defining a chute-like path therebetween for receiving and confining said article therealong, each cylindrical member being provided with helical means for engaging said rim of said article, the feed rates of all of said helical means at any given point along the chute-like path being identical at such point with the exception of a section of the helical means of one cylindrical member, said section having a different feed rate from the corresponding feed rate at the same point along the chute-like path of the other helical means for canting the article as it passes said section.
 11. Apparatus according to claim 10, wherein said three cylindrical members have helical means with the same diameters and are coupled for rotation at the same speed, the leads of all of said helical means at any given point along the chute-like path being identical with the exception of said section of the helical means of said one cylindrical member.
 12. The method of imprinting the sidewall of a cup-like article which comprises the steps of feeding said articles in a nested stack toward a printing zone, partially separating said articles as they approach the printing zone to expose a region of the sidewall for printing, and imprinting said region of each article as it passes the printing zone while the articles are in partially nested condition.
 13. The method of claim 12, further comprising the step of canting each article after said partial separation to bring an element of a tapered sidewall in parallel with the direction of travel past the printing zone.
 14. Printing apparatus comprising a printing plate mounted for rotation about a predetermined axis, said plate having a pattern printing surface extending helically around saId axis and facing radially outwardly therefrom, drive means for rotating said plate around said axis and thereby moving each portion of said printing surface in a circumferential direction around said axis and feeding means for engaging the surface of a medium to be printed on with said printing surface and for simultaneously moving the portion of said surface of said medium which engages said printing surface both in the same direction and at the same rate as the portion of said printing surface which it engages is moved, thereby to cause them to move without slippage therebetween, and in a direction parallel to the direction of said axis.
 15. Apparatus according to claim 14 further comprising a second printing plate having a second pattern printing surface mounted for rotation co-axially with said first-mentioned printing plate but spaced axially therefrom, said second printing surface extending helically around said axis and facing radially outwardly therefrom, drive means for rotating said second plate around said axis and thereby moving each portion of said printing surface in a circumferential direction around said axis and feeding means for engaging the surface of a medium to be printed with said printing surfaces and for simultaneously moving the portion of said surface of said medium which engages said printing surfaces both in the same direction and at the same rate as the portions of said printing surfaces which it engages are moved, thereby to cause them to move without slippage therebetween, and in a direction parallel to the direction of said axis.
 16. Apparatus according to claim 15 further comprising first means for inking one of said printing surfaces, and second means for inking the other of said printing surfaces.
 17. Apparatus according to claim 14, wherein the medium to be printed has a print receiving surface represented by a surface of revolution with a straight line generatrix, and said feeding means comprises means for orienting said medium such that its print receiving surface makes rolling line contact with said printing surface. 